The present disclosure relates to image forming apparatuses.
In image forming apparatuses, such as a copier and a printer, configured to form an image by electrophotography, an image is formed on a sheet through a specified electrophotographic process. In this electrophotographic process, the surface of an image carrier, such as an organic photosensitive drum, is charged with electricity by applying a voltage to a contact charging member, such as a charging roller, in contact with the image carrier, the charged image carrier is exposed to image-bearing laser light to form an electrostatic latent image, and the electrostatic latent image is developed with a developer toner by a developing device and thus formed into a toner image.
The toner image is transferred to a recording medium, such as a paper sheet, or an intermediate transfer member, a photosensitive layer on the surface of the image carrier after being subjected to the transfer process is cleaned by a cleaning blade, residual charge on the photosensitive layer is removed by optical static elimination, and then the process returns to the charging step. This process cycle is repeated. Meanwhile, the recording medium having the toner image transferred thereto passes through a fixing unit including a roller heated to a predetermined temperature to fix the toner image on the surface thereof and is then discharged to the outside of the image forming apparatus.
Generally, the optimal setting values for process conditions (a charging bias condition, a transfer bias condition, a development bias condition, fixing control, and so on) during image formation vary depending upon the temperature, humidity, and so on in the surrounding environment. For example, under high-temperature environment, the transfer performance decreases owing to moisture adsorption of the paper. Therefore, to secure the transferability, the transfer voltage applied needs to be increased. For another example, organic photoconductors generally change the ability to be charged depending upon the temperature. Therefore, to maintain a constant charged potential of such a photoconductor independent of the temperature, the charging bias applied needs to be changed according to the temperature.
To solve the above problems, a large number of techniques are disclosed in which a temperature sensor and a humidity sensor are provided in the interior of an image forming apparatus and the conditions for the image forming process are changed based on detection results of these sensors. In a general image forming apparatus, external air is introduced thereinto via a fan or the like for the purpose of cooling the image forming section and the temperature and humidity sensors are exposed to the external air having passed through the fan or the like to increase the response of the detected values.
There is also known a technique in which a substrate having one surface with a temperature sensor placed thereon and the other surface with a humidity sensor placed thereon is disposed at an intake opening in a sirocco fan so that intake air is allowed to flow in parallel flows over the one and the other surfaces of the substrate. With this technique, the distance from the intake opening to the temperature sensor can be equal to the distance from the intake opening to the humidity sensor. Thus, the temperature sensor and the humidity sensor can detect the external air flows in the same conditions, resulting in further reduced reading errors between the sensors.